Combined radioreceiver, electrical phonograph, and public address system



MAIBOHM 1,868.613 COMBINED RADIORECEIVER, ELECTRICAL PHONOGRAPH,

2 Sheets-Sheet *1 h INVENTOR.

may 6, rawofz/ ATTORNEY.

AND PUBLIC ADDRESS SYSTEM Filed 001;. 30, 1929 July 26, 1932.

1,868,613 ELECTRICAL PHONOGRAPH, ADDRESS SYSTEM t. 50, 1929 2Sheets-Sheet 2 y 1932- H. c. MAIBOHM COMBINED RADIORECEIVER AND PUBLICFiled 00 INVENTOR. 5% (1 famed/606444 M I UH H m HH ATTORNEY PatentedJuly ,26, 1932 UNITED: STATES.

PATENT OFFICE HARRY C. MAIBOHM, OF SANDUSKY, OHIO, ASSIGNOR TO THESIMPLEX RADIO COM- PANY, OF SANDUSKY, OHIO, .A CORPORATION OF OHIOCOMBINED RADIORECEIVER, ELECTRICAL PHONOGRAPH, AN D PUBLIC ADDRESSSYSTEM Application filed October 30, 1929. Serial No; 403,474,

My invention relates broadly to sound reproducing apparatus and moreparticularly to a. circuit arrangement for a combined public addresssystem, electric phonograph, and radio broadcast receiver.

One of the objects of my invention is to provide a compact constructionof apparatus which may be employed at the election of the operator as apublic address system or as an electric phonograph for the reproductionof sound records or as a radio broadcast receiver under control of aswitching system which employs the circuits of the apparatus in theenumerated arrangements.

Another object of my invention is to provide a circuit arrangement forthe audio frequency amplifier portion of a radio broadcast receiversystem with a selector switch arranged to alternately connect amicrophone circuit or electric phonograph circuit with the input systemof the audio frequency amplifier for employing the audio frequencyamplifier circuits and sound reproducing system of the radiobroadcastreceiver either in their normal arrangement as part of. a radiobroadcast receiver or alternately as a public address system or. anelectric phonograph reproducer.

My invention finds particular application in schools, hotels, factories,resorts, theaters, and other places of public assembly where asimplified apparatus is desired for the amplification of sound.

The circuit arrangement of the apparatus of my invention has been foundto be ex tremely practical and successful in its operation and it willbe understood more clearly from the specification hereinafter followingby reference to the accompanying drawings, in which:

Figure 1 diagrammatically illustrates the combination publicaddress-electric phonograph and radio broadcast system of my invention;Fig. 2 shows diagrammatically the position of the selector switchforutilizing the amplifier circuits of the radio broadcast receiver as partof the public address system; Fig. 3 illustrates the position of theselector switch when the audio frequency amplifier portion of thereceiver is employed as an electric phonogra h; and Fig. 4 shows theposition of the se ector switch when the audio frequency amplifierandsound reproducer is employed as a radio broadcast receiver.

Referring to the drawings in detail, the radio frequency amplifierstages of the radio broadcast receiver are designated by referencecharacters 1, 2 and 3. The detector stage is shown at 4. The first stageof audio frequency amplification is indicated at 5 which connectsthrough transformer 27 with the push-pull amplifier system designated at6 and 7 the output circuit of which connects to the sound reproducer 10.The radio broadcast receiver is connected to an antenna 8 and groundconnection 9. The power is supplied for the several electron tubes topower transformer 11 having a primary winding 14 and secondary windings18, 19, 20, 21 and 22. The primary winding 14 connects to thealternating current power supply line 12, fuse 17, and switch 15, whichis arranged to select the entire primary winding 1 or a tap l6 thereon.The rectifier tubes for the power supply line apparatus are shown at 23and 24 connected with the power transformer system and to the filtercircuit 25 for delivering rectified alternating current to potentiometer26 from which the energy is supplied to the plate circuits ofthe severaltubes of the amplifier system. i The control switch for the apparatus isshown at 30 and consists of a cam member having a central position ormovable to either of two opposite positions. The cam switch includesresilient arms30a, 30b, 30c, and 30d which are shiftable by movement ofthe cam 30 with respect to associated sets of contacts. Resilient arm30a is associatedwith front and back contacts 31a and 316, respectively.Resilient arm 30?) is associated with front and back contacts 32a and326, respectively. Resilient arm 300 is associated with frontand backcontacts 836 and 33a, respectively. Similarly, resilient arm 30d isassociated with front and back contacts 346 and 3411, respectively. Thenormal position for the resilient arms is in contact with the sets ofback contacts and when the cam 30 moves out of the pathof the reilientarms, the arms return to contact with the back contacts as enumerated.

The public address system includes a double microphone circuit shown at45, the central terminal of which is connectihle through adjustablerheostat 46, meter 47, battery 48, switch 49 with the resilient arm 30a.The opposite terminals of the microphone 45 connect to the ends of theprimary winding 36 of transformer The midpoint of primary winding 36 isgroinidedaiul is connected to the front contact 81a as illustrated inFig. 1 of the drawings. The microphone circuit is therefore completewhen cam 30 is in the position shown in Figure l with resilient arms 30amoved to establish connection with contact 31a as shown more clearly inFigure 2. Under this condition, resilient arm 2305 establishesconnection with contact 32a and shunts the phonograph pick-up circuit 42to ground by a connection at 51 to contact 32a and a connection at 44from the phonograph pick-up system. Under these same conditions it willbe observed that the primary winding 37 used as part of the electricphonograph circuit is open circuited through contact arm 30d andcontacts 34a and 325 at one end, and through contact arm 30c, contact38a, and ground 50 at the opposite end. The secondary winding oftransformer 35 which is shown at 3060 connects to ground 39 at one end,and to the grid of the electron tube 5, constituting the first stage ofaudio frequency amplification at the other end. The ground 3960 at thecathode of electron tube 5 completes the connection through ground 39 tothe other end of secondary winding 38. The energy from the microphonecircuit 45 therefore passes through the switch system with the cam 30shown in the position illustrated in Figure 1 to the pushpull amplifier6-7 through transformer 27 for actuating the sound reproducer 10. Underthis condition, the detector output of tube 4 in the radio broadcastreceiver is not impressed upon the first stage of audio frequencyamplification for the plate system of the detector tube is open as willbe observed by tracing the lead 41 from the plate terminal of tube 4 tocontact 34?) and the connection from contact 335 to the point 26a inpotentiometer 26. Under these conditions, there will be no interferencefrom the radio broadcast receiver in the sound reproducing system whenthe microphone circuit is connected to the inputof the audio frequencyamplifier system. However, all of the tubes in the radio broadcastreceiver are maintained in operating condition so it is possible toswitch instantly to any one of the three positions of the selectorswitch without waiting for the cathodes to heat.

When it is desired to utilize the apparatus as an electric phonograph,the selector switch is moved to the position illustrated in Figure 3where the resilient arms 30a, 30b, 50c, and 3065 each establishconnection with the back contacts 31b, 32b, 33a, and 34a, respectively.This operation immediately opens the circuit to the microphone system 45by breaking the connection between arm 30a and contact 3161.. Likewise,the phonograph pick-up 42 is immediately placed in circuit with theprimary winding 37 of transformer 35 through arm 30?), contact 8527;.contact 34a, arm 30%, secondary winding 3?, arm 30c, contact 3364, andground 50, the other end of the phonograph pickup being grounded at 44.To insure continuous performance and guard against interruption in thereproduced program, I provide two phonograph turntables d1: Jen byindependent motor systems as represented at 40 and 41 each receivingsound records which actuate the phonograph piclr-up devices 42 and 43,respectively. A selector switch is provided for cutting in the drive 41.and the pick-up 43 when the second phonograph is to be connected foroperation. power being obtained from the line system 12. A main switch54 may be provided to cut oil the power to the motor circuit. Vith theswitch in the position shown in F igure 3, it will be observed that thedetector tube 4 is isolated from plate potential by the existence of theopen circuit between the plate lead 40, which connects to contact 34?)and the connection from 837) which extends to the source of platepotential at 26a. Similarly, the microphone circuit is opened so thatthe audio frequency amplifier receives energy from the electricphonograph through secondary winding 38 of transformer direct to theinput circuit of tube 5.

\Vhen it is desired to employ the apparatus I as a radio broadcastreceiver, switch 30 is moved to the position shown in Figure 4 whichserves to close the plate circuit of the detector tube from lead. 4a.contact 347), resiL ient arm 30d, primary winding 37, contact arm 300,contact member 337), returning to the source of positive potential atpoint 26m 011 potentiometer 26. At the same time, the electricphonograph is open circuited by reason of the fa .t that contact arm30?) connects to contacts 326 and 34a which are at zero potential.Similarly. the microphone circuit is open for battery circuit 48terminates at resilient arm 30a which is in contact with the floatingcontact member 317). It will be observed that the same transformersystem 35 is utilized as the coupling transformer between the outputcircuit of the detector 4 and the input circuit of the first stage ofaudio frequency amplification as well as coupling means between themicrophone circuit and the input of the audio frequency amplitiersystem, and also as the means for transferring energy from thephonograph pick-up circuit to the input system of the audio frequencyamplifier. By throwing the switch ice 30 to any one of the positionsillustrated in Figures 2, 3 and 4c, the particular .service which isdesired from the apparatus is read ily selected.

The apparatus of my invention has proven highly practical and successfulin operation. In modern school systems it is possible for announcementsand lectures to begiven through the microphone circuit to an entirestudent body and the sound distributed over a large area. The output ofthe apparatus may be connected to a multiplicity of sound reproducingdevices connected in parallel with the sound reproducer 10 which arelocated in various rooms of an educational institution. In this way,phonograph music, an address, or a radio broadcast program may bedelivered to the occupants of the different rooms.

In a hotel system my apparatus has been found to be practical in that acentral installation may be made and the radio broadcast music orelectric phonograph programs distributed to guests in hundreds of roomsthroughout a hotel building. Executives may address the employees of afactory through a huge organization by distributing loud speakersthroughout the building electrically connected in parallel with thespeaker circuit 10, the apparatus and microphone being located in theexecutives ofiice. The same method may be employed in locatingindividuals in remote parts of a large plant. My invention also findsapplication in resorts, amusement parks, and other places of publicassembly in the distribution of sound over a large area.

While I have described the circuit arrangement of the apparatus of myinvention in one of its preferred embodiments, I desire that it beunderstood that modifications may be made and that no limitations uponmy invention are intended other than are imposed by the scope of theappended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. In a sound reproducing system, a radio receiver including a detectorand an audio frequency amplifier, a sound reproducer conwindings for oeration of said sound reproducer indepen ent of the operation of saiddetector.

2. In a sound reproducing system, a radio receiver including a detectorand audio frequency amplifier, a sound reproducer connected to theoutputcircuit of said audio frequency amplifier, a coupling systembetween said detector and the input circuit of said audio frequencyamplifier including a secondary winding connected across the inputcircuit of said audio frequency amplifier and a pair of secondarywindings, a switching device connected with said primary windings, anelectric phonograph circuit, said switching device being common to allof said circuits, a microphone circuit, connections between saidswitching device and said electric phonograph circuit, and means forcompleting connection through said switching device between the other ofsaid primary windings and said microphone circuit for effecting theoperation of said sound reproducer independent of the operation of saiddetector.

In testimony whereof I alfix my signature.

HARRY G. MAIBOHM.

nected to the output circuit of said audio frequency amplifier, atransformer having a secondary winding connected with the input circuitof said audio frequency amplifier and a pair of primary windings, amicrophone circuit, an electric phonograph circuit, a switching devicecommon to all of said circuits, connections between said electricphonograph circuit and said switching device, said switching deviceoperating to disconnect said detector from said audio frequencyamplifier, and selectively complete connections between said microphonecircuit and one of said primary windings, or selectively completeconnections between said electric phonograph circuit and the other ofsaid primary

